Programmatically change ConstraintSet attribute in motion scene of MotionLayout

What you can do is access the ConstraintSet and then set the ratio:

motionLayout.getConstraintSet(R.id.start)?.let { startConstraintSet ->
    val ratio = imageView.calculateRatio()
    startConstraintSet.setDimensionRatio(R.id.top_image_container, ratio)
    // You can set the width and height here as well
}